Photocrosslinkable transparent adhesive material, transparent adhesive material layered body, and layered body for constituting optical device

ABSTRACT

Provided is a novel transparent adhesive material having low relative permittivity as well as excellent adhesive characteristics, whereby an olefinic polymer resin layer and an acrylic polymer adhesive layer can be suitably integrated. Suggested is a transparent adhesive material provided with an outermost surface layer containing an acrylic polymer (B) and a photocrosslinking initiator, and an intermediate layer containing an olefinic polymer (A), a crosslinking agent, and a photocrosslinking initiator, in which the intermediate layer contains a (meth)acrylate monomer as the crosslinking agent.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 15/507,645, filed on Feb. 28, 2017, which is a national stage entryof International Application PCT/JP2015/076480, filed on Sep. 17, 2015,and claims foreign priority from Japanese Patent Application No.2014-189989, filed on Sep. 18, 2014, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a transparent adhesive material havinglow permittivity as well as excellent adhesive characteristics. Inparticular, the invention relates to a transparent adhesive materialwhich can be suitably used for attachment of devices such as an opticaldevice including a mobile terminal (PDA) like a smart phone, a tabletcomputer, a personal computer (PC), a game machine, a television (TV), acar navigation system, a touch panel, a pen tablet, and an organic ELelement, or a solar cell module like an organic thin film and a pigmentsensitization, or members constituting module, and relates to atransparent adhesive material layered body and a layered body forconstituting an optical device using the transparent adhesive material.

BACKGROUND ART

Conventionally, in order to improve the visibility of an optical device,a gap between an image display panel such as a liquid crystal display(LCD), a plasma display panel (PDP), or an electroluminescence display(ELD) and a member of a protective panel or touch panel, which isdisposed on the front side (viewing side) thereof, is filled with anadhesive sheet or an liquid-phase adhesive so as to suppress thereflection of incident light or light emitted from a display image at anair layer interface.

As a method for filling the gap between members for constituting thoseoptical devices with an adhesive, a method of filling a liquid-phaseadhesive resin composition containing an UV ray curable resin in the gapand performing irradiation of ultraviolet ray for curing is known(Patent Document 1).

In recent years, thinning and reducing weight are in progress in thefield of an optical device, in particular, a cellular phone, a portableterminal, or the like, and new problems arise accordingly. Namely, in anoptical device provided with a touch sensor function, in particular, atouch function of capacitance type which is widely distributed, thecapacitance of a capacitor which is formed between two electrodes thatface each other via an insulating film changes according to touch of aconductor like a finger at a surface protective panel side to detect theposition. However, according to the thinning of a member, a gap betweenthe electrode and protective panel surface is reduced and the change incapacitance responding to touch increases, and thus a problem arises inthat noise easily occurs in detection signal.

Furthermore, in addition to the thinning and reducing weight of amember, thinning of a filling member used for integration of a memberlike adhesive sheet is also required due to shrinking gaps among themembers. As such, for absorbing a change in sensitivity of touchdetection that is caused by a member or thinning of the sheet itself,there is a need for the adhesive sheet used for filling a gap between anelectrode and a surface protective panel to have low permittivity.

Furthermore, in view of the reducing weight or cost of an electrode, asan electrode substrate, glass is currently being replaced with a resinfilm. In the case of an electrode in which a conductive film is formedby pattern forming only on a single surface, it is necessary to layertwo film electrodes or a glass electrode and a film electrode via anadhesive sheet or the like, and it is also required that an adhesivematerial layer used for such case has low relative permittivity.

As an adhesive material with low relative permittivity, an adhesivesheet for optical use using a composition which contains a monomercomponent including specific (meth)acrylic acid alkyl ester with arelatively long-chain alkyl group or alicyclic hydrocarbon group isdisclosed in Patent Document 2, for example.

In Patent Document 3, an adhesive composition with low permittivityusing an acrylic ester copolymer which is obtained by copolymerizationof a methacrylic acid ester monomer having specific carbon atom numberin a side chain, in which the adhesive composition is particularlysuitable for attachment of a touch panel, is disclosed.

In Patent Document 4, as a composition for an adhesive sheet by which anadhesive sheet with low permittivity and low dissipation factor can beformed, a composition for an adhesive sheet containing an elastomerwhich consists of polyphenylene ether and a styrene butadiene copolymerand triallyl isocyanurate is disclosed.

In Patent Document 5, a thermoplastic resin composition which has apolyphenylene ether-based polymer having hydroxyl groups in the chemicalstructure thereof and having 2,6-dimethylphenylene ether as a repeatingunit, any one of an isocyanate compound having plural isocyanate groupsin the structure thereof and a hydrogenated styrene-based elastomer, ora reaction product thereof is disclosed.

CITATION LIST Patent Document

Patent Document 1: WO 2010/027041 A

Patent Document 2: JP 2012-173354 A

Patent Document 3: JP 2013-001761 A

Patent Document 4: JP 2000-104038 A

Patent Document 5: JP 2012-041372 A

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

An olefinic polymer having no highly polar group such as polyethylene orpolypropylene is known with electrical characteristics that it has lowrelative permittivity and excellent dielectric characteristics, inparticular. As such, an adhesive material containing the aforementionedolefinic polymer as a main component is known to exhibit excellentdielectric characteristics.

However, the adhesive material containing the olefinic polymer as a maincomponent has a relatively low adhesion property in general and thusdoes not have sufficient adhesion property for attachment of a memberwhich constitutes an optical device as described above.

As a method for solving the above problems, it may be considered tolayer an adhesive layer having an acrylic polymer as a main component onone side or both sides of a resin layer which contains an olefinicpolymer as a main component.

However, as the olefinic polymer and the acrylic polymer are thematerials that are intrinsically difficult to attach, there is a problemthat, when a resin layer containing an olefinic polymer as a maincomponent and an adhesive layer containing an acrylic polymer as a maincomponent are desired to be layered, it remains difficult to achieve theintegration.

Accordingly, in order to provide a transparent adhesive material havinglow relative permittivity as well as excellent adhesive characteristics,the invention is intended to provide a novel transparent adhesivematerial having a constitution that an adhesive layer containing anacrylic polymer as a main component is layered on one side or both sidesof a resin layer containing an olefinic polymer as a main component,whereby the resin layer containing an olefinic polymer as a maincomponent and the adhesive layer containing acrylic polymer as a maincomponent can be suitably integrated.

Means for Solving Problem

Suggested by the invention is a photocrosslinkable transparent adhesivematerial provided with an outermost surface layer containing an acrylicpolymer (B) and a photocrosslinking initiator, and an intermediate layercontaining an olefinic polymer (A), a crosslinking agent, and aphotocrosslinking initiator, in which the intermediate layer contains a(meth)acrylate monomer as the crosslinking agent.

Also suggested by the invention is a transparent adhesive materialprovided with an outermost surface layer containing a photoreactionproduct of an acrylic polymer (B), and an adjacent intermediate layercontaining a photoreaction product of an olefinic polymer (A), in whichrelative permittivity is 3.3 or less at a frequency of from 100 kHz to 1MHz.

Effect of the Invention

In the photocrosslinkable transparent adhesive material suggested by theinvention, an intermediate layer containing an olefinic polymer (A) isused, and thus the adhesive material as a whole can have loweredrelative permittivity.

Furthermore, as the photocrosslinkable transparent adhesive material isprovided with an outermost surface layer containing an acrylic polymer(B) and a photocrosslinking initiator, the adhesive characteristics canbe enhanced compared to a monolayer adhesive material containing theolefinic polymer (A) as a main component. Further, in view of thehistory of a related art, it can be used for attachment of a member forconstituting an optical device.

Furthermore, in the photocrosslinkable transparent adhesive materialthat is suggested by the invention, by adjusting the 130° C. meltviscosity of a resin composition for constituting the intermediate layercontaining an olefinic polymer (A) and the same of a resin compositionfor constituting the outermost surface layer containing an acrylicpolymer (B) to be within a predetermined range, the resin compositionscan be heated and melt at the same temperature. Accordingly, it ispossible to perform coextrusion, for example, and the interfaceadhesiveness between the two layers can be enhanced.

In that case, by containing a (meth)acrylate monomer as a crosslinkingagent in the above intermediate layer, the (meth)acrylate monomer in theintermediate layer can diffuse and permeate into the outermost surfacelayer containing an acrylic polymer (B) or an interaction of theoutermost surface layer occurs according to a reaction of thecrosslinking agent contained in the intermediate layer when acrosslinking reaction is allowed to occur by irradiation of light, andthus the interface adhesiveness between the two layers can be furtherenhanced.

MODE(S) FOR CARRYING OUT THE INVENTION

Hereinbelow, an example of embodiments of the invention is described indetail. However, it is evident that the invention is not limited to thefollowing embodiments.

<Present Transparent Adhesive Material>

The photocrosslinkable transparent adhesive material according to thisembodiment (hereinbelow, referred to as “the present transparentadhesive material”) is a transparent adhesive material provided with anoutermost surface layer containing an acrylic polymer (B) and aphotocrosslinking initiator, and an intermediate layer containing anolefinic polymer (A), a crosslinking agent, and a photocrosslinkinginitiator.

As for the present transparent adhesive material, it is preferable that130° C. melt viscosity η of the resin composition for constituting theabove outermost surface layer and the above intermediate layer is 5×10¹to 5×10³ Pa·s and the ratio η_(a)/η_(b) between melt viscosity η_(a) ofthe outermost surface layer and melt viscosity η_(b) of the intermediatelayer is 0.05 to 20.

As the 130° C. melt viscosity η_(b) of the resin composition forconstituting the intermediate layer containing the olefinic polymer (A)and the 130° C. melt viscosity η_(a) of the resin composition forconstituting the outermost surface containing the acrylic polymer (B)are adjusted to be within a predetermined range, similar viscositycharacteristics can be exhibited at the same temperature. Thus, forexample, as the adhesion property between the layers is enhanced duringintegration by coextrusion or thermal lamination, the interfaceadhesiveness between the two layers can be enhanced.

From the above point of view, the 130° C. melt viscosity η of the resincomposition for constituting the outermost surface layer and theintermediate layer is preferably 5×10¹ to 5×10³ Pa·s. As it is 5×10¹Pa·s or more, preparing a sheet by heating can be easily achieved, andas it is 5×10³ Pa·s or less, the adhesion property between the layerscan be maintained and it is easy to have integration by layering, andtherefore desirable. In particular, it is preferable that the 130° C.melt viscosity η is 7×10¹ Pa·s or more or 3×10³ Pa·s or less, and moreparticularly, 1×10² Pa·s or more or 1×10³ Pa·s or less.

Furthermore, from the same point of view as above, it is preferable thatthe ratio η_(a)/η_(b) between the outermost surface layer melt viscosityη_(a) and the intermediate layer melt viscosity η_(b) of the resincomposition for constituting the outermost surface layer and theintermediate layer is preferably 0.05 to 20. In particular, it is morepreferably 0.07 or more or 15 or less, even more preferably 0.1 or moreor 10 or less, and still even more preferably 0.2 or more or 5 or less.

As a method for adjusting the 130° C. melt viscosity of the resincomposition for constituting the intermediate layer containing theolefinic polymer (A) and the 130° C. melt viscosity of the resincomposition for constituting the outermost surface containing theacrylic polymer (B), there is a method of adjusting the molecular weightof the resin, which is a main component of each resin composition, thatis, the olefinic polymer (A) and the acrylic polymer (B).

From the above point of view, the weight average molecular weight (Mw)of the olefinic polymer (A) is 50,000 to 400,000, preferably 60,000 ormore to 200,000 or less, and more preferably 70,000 or more or 150,000or less.

Meanwhile, the weight average molecular weight (Mw) of the acrylicpolymer (B) is 100,000 to 800,000, preferably 150,000 or more to 550,000or less, and more preferably 200,000 or more or 500,000 or less.

It is also possible to adjust the melt viscosity by increasing ordecreasing the blending amount of other addition components such as acrosslinking agent or a photocrosslinking initiator. The preferredcomposition and addition amount of addition components will be describedlater.

<Intermediate Layer>

The intermediate layer is described hereinbelow.

The intermediate layer is a layer which contains at least the olefinicpolymer (A), a crosslinking agent, and a photocrosslinking initiator.

It is preferable that the intermediate layer has relative permittivityof 3.0 or less at a frequency of from 100 kHz to 1 MHz or less.

As the intermediate layer has the relative permittivity within the aboverange, it becomes easier to provide the present transparent adhesivematerial with excellent electrical characteristics.

From the above point of view, the relative permittivity of theintermediate layer is preferably 3.0 or less, more preferably 2.8 orless, and even more preferably 2.6 or less at a frequency of from 100kHz to 1 MHz or less.

Furthermore, to adjust the relative permittivity of the intermediatelayer to be within the above range, it is preferable to select and use aresin described below as the olefinic polymer (A).

(Olefinic Polymer (A))

Examples of the olefinic polymer (A) which is used for the intermediatelayer include an ethylene-α-olefin copolymer, a styrene-based elastomer,a polyisobutylene resin, a polybutene resin, a polybutadiene resin, apolyisoprene resin, and an ethylene.cyclic olefin copolymer, and it isalso preferable to use it either singly or in combination of two or moretypes thereof.

Among them, from the viewpoint of the electrical characteristics, watervapor barrier property, transparency, flexibility, sheet processability,weather resistance and reliability, or the like of a transparentadhesive material, it is particularly preferable to use any one type ofan ethylene-α-olefin copolymer, a styrene-based elastomer, and apolyisobutylene resin, or combination of two or more types of them.

In that case, it is also possible to use combination of two or moretypes of the olefinic polymer with different composition or differentmolecular weight.

It is sufficient for the above “ethylene-α-olefin copolymer” to be acopolymer of ethylene and α-olefin.

Type of the α-olefin to be copolymerized with ethylene is notparticularly limited.

In general, α-olefin with carbon atom number of 3 to 20 can be suitablyused. Examples thereof include propylene, 1-butene, 1-pentene, 1-hexene,1-heptene, 1-octene, 1-nonene, 1-decene, 3-methyl-butene-1, and4-methyl-pentene-1. Among them, from the viewpoint of the ease ofindustrial obtainability, economic efficiency, or the like, as anα-olefin, a copolymer containing 1-butene, 1-hexene, or 1-octene as acopolymerization component is preferable. In that case, the α-olefin tobe copolymerized with ethylene can be used either singly or incombination of two or more types thereof at any ratio.

Furthermore, content of the α-olefin to be copolymerized with ethyleneis not particularly limited. For example, relative to the entire monomerused for copolymerization, it is preferably 2% by mol to 40% by mol,more preferably 3% by mol or more or 30% by mol or less, and even morepreferably 5% by mol or more or 25% by mol or less. As the content ofthe α-olefin to be copolymerized with ethylene is within the aboverange, the crystallinity is reduced due to the copolymerizationcomponent and the transparency (for example, total light transmittance,haze, or the like) is enhanced, and therefore desirable. Furthermore, asthe content of the α-olefin to be copolymerized with ethylene is withinthe above range, an occurrence of blocking or the like is suppressedduring the production of raw material pellets, and thus desirable.

Furthermore, the type and content of the α-olefin to be copolymerizedwith ethylene can be analyzed by a known method, for example, by using anuclear magnetic resonance (NMR) analyzer or other instrumentalanalyzer.

The aforementioned ethylene-α-olefin copolymer may also contain amonomer unit that is derived from a monomer other than α-olefin.

Examples of the monomer unit include cyclic olefin, a vinyl aromaticcompound (styrene or the like), and a polyene compound.

Content of the monomer unit is, when the entire monomer unit in anethylene-α-olefin copolymer is 100% by mol, preferably 20% by mol orless, and more preferably 15% by mol or less.

Furthermore, the stereo structure, branching, branch distribution,molecular weight distribution, or copolymerization mode (random, block,or the like) of an ethylene-α-olefin copolymer are not particularlylimited. However, a copolymer with a long-chain branch, that is, acopolymer having a branch in the main chain itself, has advantages thatthe mechanical properties are generally favorable and a calender moldingproperty is enhanced due to high melt tension during film molding.

The ethylene-α-olefin copolymer may or may not have a crystal fusionpeak. Upper limit of the crystal fusion peak is not particularlylimited. Considering the transparency or flexibility at low temperature,it is preferably 100° C. or less, more preferably 80° C. or less, andeven more preferably 65° C. or less. Furthermore, lower limit of thecrystal fusion peak is, considering prevention of blocking of rawmaterial pellets, handling property of an adhesive material, or shapemaintaining performance at room temperature or the like, preferably 20°C. or more, more preferably 30° C. or more, and even more preferably 40°C. or more. Furthermore, there may be plural crystal fusion peaks.

Crystal fusion heat of the ethylene-α-olefin copolymer is notparticularly limited. It is preferably 0 to 100 J/g, more preferably 5J/g or more or 80 J/g or less, and even more preferably 10 J/g or moreor 65 J/g or less. As it is within the above range, flexibility,transparency, or the like can be ensured, and thus desirable.

Furthermore, the above crystal fusion peak or crystal fusion heat can bemeasured by using a differential scanning calorimeter (DSC) at heatingrate of 10° C./min in view of JIS K7121.

MFR (JIS K7210: temperature of 190° C. and a load of 21.18 N) of theethylene-α-olefin copolymer is not particularly limited. It ispreferably 5 g/10 min to 60 g/10 min, more preferably 8 g/10 min or moreor 50 g/10 min or less, and even more preferably 10 g/10 min or more or45 g/10 min or less.

As for the ethylene-α-olefin copolymer, an ethylene-α-olefin copolymerwith density of 0.850 to 0.900 g/cm³ is preferable to have excellenttransparency, low temperature characteristics, or the like. Anethylene-α-olefin copolymer with density of 0.860 to 0.885 g/cm³ (linearshaped low density polyethylene) is more preferable.

Among the ethylene-α-olefin copolymers, an ethylene-α-olefin randomcopolymer is even more preferable from the viewpoint of having excellentlight transmittance and flexibility. They may be used either singly oras a mixture of two or more types thereof.

The method for producing the above ethylene-α-olefin copolymer is notparticularly limited and a known polymerization method using a knowncatalyst for ethylene polymerization can be employed. Examples of aknown polymerization method include a slurry polymerization method, asolution polymerization method, a vapor phase polymerization method, ora bulk phase polymerization method using radical initiator in which amulti-site catalyst represented by Ziegler.Natta type catalyst or asingle-site catalyst represented by metallocene-based catalyst or a postmetallocene-based catalyst is used.

From the viewpoint of having easy granulation (pelletization) afterpolymerization or prevention of blocking of raw material pellets, it ispreferable to have the production by using a polymerization method inwhich a single-site catalyst allowing less content of low molecularweight component and polymerization of raw materials with narrowmolecular weight distribution is used.

Examples of the aforementioned “styrene-based elastomer” include SBR(styrene-butadiene rubber), SIB (styrene-isobutylene rubber), SBS(styrene-butylene-styrene block copolymer), SIS(styrene-isobutylene-styrene block copolymer), SEBS(styrene-ethylene-butylene-styrene block copolymer), SEBC(styrene-ethylene-butylene-ethylene block copolymer), SIB(styrene-isobutylene block copolymer), and HSBR (hydrogenated styrenebutadiene rubber).

Content of the styrene in the styrene-based elastomer is notparticularly limited. From the viewpoint of weather resistance, forexample, it is preferably 20% by mol or less relative to the entiremonomer component for constituting the elastomer.

MFR (JIS K7210: temperature of 190° C. and a load of 21.18 N) of thestyrene-based elastomer is not particularly limited. It is preferably 5g/10 min to 100 g/10 min, more preferably 8 g/10 min or more or 80 g/10min or less, and even more preferably 10 g/10 min or more or 50 g/10 minor less.

It is sufficient that the aforementioned “polyisobutylene resin” is aresin which has a polyisobutylene skeleton in the main chain or sidechain. Examples thereof include a homopolymer of an isobutylene monomer,a copolymer of isobutylene and a small amount of isoprene, and acopolymer of isobutylene and n-butane or butadiene.

Viscosity average molecular weight (Mv) of the polyisobutylene resin isnot particularly limited. It is preferably 50,000 to 400,000, morepreferably 70,000 or more or 300,000 or less, and even more preferably100,000 or more or 200,000 or less. By having the viscosity averagemolecular weight (Mv) within the above range, it is easy to satisfysimultaneously the processability, the shape stability of a sheet, heatresistance for practical use or the like.

It is possible that the olefinic polymer (A) has a functional group. Byusing an olefinic polymer with a functional group, not only thecompatibility with additives such as a crosslinking agent and aphotocrosslinking initiator or an anti-oxidant can be enhanced but alsothe adhesion strength to a subject for adhesion or other layers can beenhanced. Furthermore, although it may be used either singly or incombination with an olefinic polymer having no functional group,considering molding processability during sheet forming, economicefficiency, or the like, it is preferably used in combination with theolefinic polymer having no functional group.

As for the olefinic polymer with a functional group, at least one resinselected from the group consisting of a silane modified olefinic polymeror an acid modified olefinic polymer, an ethylene-vinyl acetatecopolymer (EVA), an ethylene-vinyl alcohol copolymer (EVOH), anethylene-methyl methacrylate copolymer (E-MMA), an ethylene-ethylacrylate copolymer (E-EAA), and an ethylene-glycidyl methacrylatecopolymer (E-GMA) is preferable.

(Crosslinking Agent and Photocrosslinking Initiator)

It is preferable for the intermediate layer to contain a crosslinkingagent and a photocrosslinking initiator.

As the intermediate layer contains a crosslinking agent and aphotocrosslinking initiator, a crosslinking reaction with the olefinicpolymer (A) can occur or a network among the crosslinking agent isformed or the like so that storage modulus G′ can be enhanced anddurability for practical use can be improved. For a long-termreliability test, for example, re-flow and a deviation, peeling, foamingor the like in members to be attached can be suppressed.

It is also preferable that a (meth)acrylate monomer is contained as acrosslinking agent in the intermediate layer. As the (meth)acrylatemonomer is contained as a crosslinking agent in the intermediate layer,the (meth)acrylate monomer in the intermediate layer can diffuse andpermeate into the outermost surface layer containing the acrylic polymer(B), or, at the time of having a crosslinking reaction by irradiation oflight, an interaction of the outermost surface layer occurs according tothe reaction of the crosslinking agent that is contained in theintermediate layer, and thus the interface adhesiveness between the twolayers can be further increased.

In that case, it is preferable that the (meth)acrylate monomer iscontained as a crosslinking agent both in the outermost surface layerand the intermediate layer, and concentration of the (meth)acrylatemonomer in the intermediate layer is higher than that in the outermostsurface layer. By having so, the (meth)acrylate monomer in theintermediate layer can more easily diffuse and permeate into theoutermost surface layer, and thus the interface adhesiveness between thetwo layers can be further increased.

The crosslinking agent used for the intermediate layer is notparticularly limited. For example, various crosslinking agents includingmonofunctional and multifunctional, functionality of two or more,crosslinking agents such as vinyl ester and (meth)acrylic acid esterwhich can have a radical crosslinking reaction can be used.

Among them, considering the compatibility with the olefinic polymer (A),transparency of an adhesive material, or the like, it is preferable toselect and use a linear aliphatic-based, a cyclic aliphatic-based, or anaromatic-based crosslinking agent. In particular, it is more preferableto use an aliphatic-based crosslinking agent with carbon atom number of6 or more or a cyclic aliphatic-based crosslinking agent. By using thosecrosslinking agents, mixing with the olefinic polymer (A) is more easilyachieved so that a deterioration of the adhesive material like phaseseparation, a decrease in the transparency, or the like can besuppressed.

Content of the crosslinking agent is, relative to 100 parts by mass ofthe olefinic polymer, 1 to 50 parts by mass, preferably 1 to 20 parts bymass, and more preferably 1 to 10 parts by mass.

Specific examples of the crosslinking agent which is used for theintermediate layer include isobornyl (meth)acrylate, lauryl(meth)acrylate, stearyl (meth)acrylate, 1,6-hexanediol di(meth)acrylate,1,8-octanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate,1,10-decanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate,butylethylpropanediol diacrylate, and tricyclodecane dimethanoldi(meth)acrylate. Those crosslinking agents may be used either singly orin combination of two or more types thereof. When two or more types ofthe crosslinking agent are used, it is preferable to use monofunctional(meth)acrylate in combination with multifunctional (meth)acrylate.Accordingly, it is possible to suppress the shrinkage during photocuringor control the compatibility with the olefinic polymer (A).

The photocrosslinking initiator in the intermediate layer can be used toplay a role of a radical generator for having a radical crosslinkingreaction of the crosslinking agent when light irradiation is carried outover a subject for adhesion after attachment of the aforementionedadhesion material.

By using the photocrosslinking initiator, photocuring can be achievedwithin a short time at low temperature. Accordingly, a damage on amember which constitutes an optical device as a member for adhesion canbe sufficiently avoided.

As for the photocrosslinking initiator, only one type or a mixture oftwo or more types of a cleave type photocrosslinking initiator which caninitiate the reaction with ultraviolet rays or visible light or ahydrogen withdrawing type photocrosslinking initiator can be used.

Type of the photocrosslinking initiator is not particularly limited.

Examples of the cleave type photocrosslinking initiator include benzoinisobutyl ether, benzyl methyl ketal, and 2-hydroxyacetophenone.

Examples of the hydrogen withdrawing type photocrosslinking initiatorinclude benzophenone, Michler's ketone, 2-ethyl anthraquinone,thioxanthone and derivatives thereof.

Content of the photocrosslinking initiator is, relative to 100 parts bymass of the olefinic polymer (A), preferably 0.3 to 10 parts by mass,more preferably 0.5 part by mass or more or 3 parts by mass or less, andeven more preferably 1.5 parts by mass or less.

(Other Resins)

For the purpose of further improving the physical properties(flexibility, heat resistance, transparency, adhesion properties, andthe like), molding processability, economic efficiency, or the like, thecomposition for forming the intermediate layer may contain a resin otherthan the above olefinic polymer (A), crosslinking agent, andphotocrosslinking initiator. Examples thereof may include an ionomerresin, a tackifying resin, and the like.

Examples of the type of the aforementioned “ionomer resin” may includean ionically crosslinkable ethylene-methacrylic acid copolymer or anionically crosslinkable ethylene-acrylic acid copolymer. The method forproducing the ionomer resin is not particularly limited. For example, itcan be carried out by neutralizing at least a portion of the unsaturatedcarboxylic acid component of a copolymer composed of ethylene, anunsaturated carboxylic acid, and another unsaturated compound as anoptional component with at least either one of a metal ion or an organicamine. In addition, the ionomer resin can be obtained, for example, bysaponifying at least a portion of the unsaturated carboxylic acid estercomponent of a copolymer composed of ethylene, an unsaturated carboxylicacid ester, and another unsaturated compound as an optional component.Specific examples thereof may include “HIMILAN” of a trade namemanufactured by DU PONT-MITSUI POLYCHEMICALS CO., LTD.

Examples of the aforementioned “tackifying resin” may include apetroleum resin, a terpene resin, a coumarone-indene resin, arosin-based resin, or any hydrogenated derivative thereof. Examples ofthe petroleum resin may include an alicyclic petroleum resin fromcyclopentadiene or a dimer thereof, or an aromatic petroleum resin froma C9 component. Examples of the terpene resin may include a terpeneresin from β-pinene or a terpene-phenol resin. Examples of thecoumarone-indene resin may include a coumarone-indene copolymer and acoumarone-indene-styrene copolymer. In addition, examples of therosin-based resin may include a rosin resin such as gum rosin and woodrosin, and an esterified rosin resin that is modified with glycerol,pentaerythritol, or the like. The content of the tackifying resin ispreferably 20 parts by mass or less and more preferably 10 parts by massor less relative to 100 parts by mass of the resin composition whichconstitutes the intermediate layer.

(Additives)

The intermediate layer may be added with various additives, ifnecessary.

Examples of the additives may include a silane coupling agent, ananti-oxidant, a weather resistant stabilizer, a processing aid, anucleating agent, an ultraviolet absorber, a flame retardant, and adiscoloration preventing agent. These additives may be used singly or incombination of two or more types thereof. Among them, a silane couplingagent, an anti-oxidant, a weather resistant stabilizer, and a processingaid will be described below.

(Silane Coupling Agent)

The silane coupling agent is useful for improving the adhesion propertyto the outermost surface layer or a peripheral member which constitutesan optical device, and examples thereof may include a compound having anunsaturated group such as a vinyl group, acryloxy group, or amethacryloxy group, and a hydrolyzable functional group such as analkoxy group as well as an amino group, an epoxy group, or the like.Specific examples of the silane coupling agent may includeN-(β-aminoethyl)-γ-aminopropyltrimethoxysilane,N-(β-aminoethyl)-□γ-aminopropylmethyldimethoxysilane,γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, andγ-methacryloxypropyltrimethoxysilane.

Among them, in the present transparent adhesive material,γ-glycidoxypropyltrimethoxysilane orγ-methacryloxypropyltrimethoxysilane can be preferably used from theviewpoint of favorable adhesion properties, decreased discoloration suchas yellowing, and the like. One type of the silane coupling agents maybe used singly or two or more types thereof may be used in combination.

The addition amount of the silane coupling agent is preferably fromabout 0.1 to 5 parts by mass or so and more preferably from 0.2 to 3parts by mass relative to 100 parts by mass of the resin composition forconstituting the intermediate layer. In addition, a coupling agent suchas an organic titanate compound can also be effectively used in the samemanner as the silane coupling agent.

(Anti-Oxidant)

The anti-oxidant is not particularly limited, and various commerciallyavailable products can be applied. Examples of the anti-oxidant mayinclude various types of anti-oxidants such as a phenol-basedanti-oxidant including a monophenol-based anti-oxidant, abisphenol-based anti-oxidant, and a polymer-type phenol-basedanti-oxidant, a sulfur-based anti-oxidant, and a phosphite-basedanti-oxidant.

Examples of the monophenol-based anti-oxidant may include2,6-di-tert-butyl-p-cresol, butylated hydroxyanisole,2,6-di-tert-butyl-4-ethylphenol, andoctadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate.

Examples of the bisphenol-based anti-oxidant may include2,2′-methylene-bis-(4-methyl-6-tert-butylphenol),2,2′-methylene-bis-(4-ethyl-6-tert-butylphenol),4,4′-thiobis-(3-methyl-6-tert-butylphenol),4,4′-butylidene-bis-(3-methyl-6-tert-butylphenol), and3,9-bis[{1,1-dimethyl-2-{β-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy}ethyl}2,4,9,10-tetraoxaspiro]5,5-undecane.

Examples of the polymer-type phenol-based anti-oxidant may include1,1,3-tris-(2-methyl-4-hydroxy-5-tert-butylphenyl)butane,1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene,tetrakis-{methylene-3-(3′,5′-di-tert-butyl-4′-hydroxyphenyl)propionate}methane,bis{(3,3′-bis-4′-hydroxy-3′-tert-butylphenyl)butyric acid}glycol ester,1,3,5-tris(3′,5′-di-tert-butyl-4′-hydroxybenzyl)-s-triazine-2,4,6-(1H,3H,5H)trione,and tocopherol (vitamin E).

Examples of the sulfur-based anti-oxidant may include dilaurylthiodipropionate, dimyristyl thiodipropionate, and distearylthiopropionate.

Examples of the phosphite-based anti-oxidant may include triphenylphosphite, diphenyl isodecyl phosphite, phenyl diisodecyl phosphite,4,4′-butylidene-bis(3-methyl-6-tert-butylphenyl-di-tridecyl)phosphite,cyclic neopentanetetraylbis(octadecyl phosphite), tris(mono- and/ordi-nonylphenyl)phosphite, tris(2,4-di-tert-butylphenyl) phosphite,diisodecyl pentaerythritol diphosphite,9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide,10-(3,5-di-tert-butyl-4-hydroxybenzyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide,10-decyloxy-9,10-dihydro-9-oxa-10-phosphaphenanthrene, cyclicneopentanetetraylbis(2,4-di-tert-butylphenyl)phosphite, cyclicneopentanetetrayl-bis(2,6-di-tert-butylphenyl)phosphite, and2,2-methylenebis(4,6-tert-butylphenyl)octylphosphite.

In the present transparent adhesive material, a phenol-based andphosphite-based anti-oxidants are preferably used from the viewpoint ofthe effect of anti-oxidant, thermal stability, economic efficiency, andthe like, and it is even more preferable to use both of them incombination since it is possible to enhance the effect as ananti-oxidant as compared to the amount added.

The addition amount of the anti-oxidant is not particularly limited, butit is preferably 0.1 part by mass to 1 parts by mass relative to 100parts by mass of the resin composition for constituting the intermediatelayer, for example, and it is more preferably 0.2 part by mass or moreor 0.5 part by mass or less, in particular.

(Weather Resistant Stabilizer)

As the weather resistant stabilizer to impart weather resistance, ahindered amine-based light stabilizer is suitably used. Examples of thehindered amine-based light stabilizer may include succinic aciddimethyl-1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethylpiperidinepolycondensate,poly[{6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl}{(2,2,6,6-tetramethyl-4-piperidyl)imino}hexamethylene{{2,2,6,6-tetramethyl-4-piperidyl}imino}],N,N′-bis(3-aminopropyl)ethylenediamine-2,4-bis[N-butyl-N-(1,2,2,6,6-pentamethyl-4-piperidyl)amino]-6-chloro-1,3,5-triazinecondensate, bis(2,2,6,6-tetramethyl-4-piperidyl) separate, and2-(3,5-di-tert-4-hydroxybenzyl)-2-n-butylmalonic acidbis(1,2,2,6,6-pentamethyl-4-piperidyl).

The addition amount of the weather resistant stabilizer is notparticularly limited, but it is preferably 0.01 part by mass or more and1 part by mass or less, more preferably 0.05 part by mass or more and0.5 part by mass or less relative to 100 parts by mass of the resincomposition for constituting the intermediate layer.

(Processing Aid)

The processing aid can be used for adjustment of the fine stickiness ofthe intermediate layer or adjustment of flow at the time of heating andmelting. For example, it is possible to appropriately select and addparaffin oil, inorganic or organic nanoparticles to the extent at whichthe transparency is not alienated.

<Outermost Surface Layer>

The outermost surface layer is a layer containing the acrylic polymer(B) and a photocrosslinking initiator, and it is preferably a layerwhich can exhibit an adhesion property.

Furthermore, the outermost surface layer preferably has higher relativepermittivity at a frequency of from 100 kHz to 1 MHz than that of theintermediate layer.

It is sufficient for the acrylic polymer (B) to be an acryl-basedpolymer which is contained in a known adhesive composition.

In particular, it is preferable to contain, as a main component, apolymer which is obtained by copolymerization of a (meth)acrylic acidester monomer and/or a vinyl ether monomer having an alkyl group.

It is preferable to use an acrylic-based, particularly, (meth)acrylicacid ester monomer (including a copolymer) as a base polymer.

Examples of the acryl monomer or methacryl monomer which is used forsynthesis of a (meth)acrylic acid ester polymer include 2-ethylhexylacrylate, n-octyl acrylate, n-butyl acrylate, and ethyl acrylate. Tothose main monomers, a crosslinkable monomer such as hydroxyethylacrylate, acrylic acid, itaconic acid, glycidyl acrylate, glycidylmethacrylate, methylol acrylamide, or maleic anhydride, or a highlyaggregating monomer or a monomer containing functional group such asmethyl methacrylate, methyl acrylate, acrylamide, acrylonitrile,methacrylnitrile, vinyl acetate, styrene, fluoroacrylate, or siliconeacrylate can be suitable added. Those monomers are polymerized by aknown polymerization method such as solution polymerization, emulsionpolymerization, bulk polymerization, or suspension polymerization. Atthat time, a polymerization initiator such as thermal polymerizationinitiator or photocrosslinking initiator may be used depending on thepolymerization method.

(Crosslinking Agent)

The outermost surface layer may be added with a crosslinking agent.

Examples of the crosslinking agent include a (meth)acryl-basedcrosslinking agent, an isocyanate-based crosslinking agent, and anepoxy-based crosslinking agent, and they may be used either singly or incombination of two or more types thereof. In particular, considering thecompatibility with an acryl-based crosslinking agent or the like, it ispreferable to use an acryl-based crosslinking agent, and it is morepreferable to use an acryl monomer which has weight average molecularweight (Mw) of 5000 or less.

Furthermore, the crosslinking agent is not limited to the(meth)acrylates that are described below, and it is also possible to useappropriately a (meth)acrylate monomer containing an organic functionalgroup, for example.

As for the (meth)acryl-based crosslinking agent, polyfunctional(meth)acrylate such as bifunctional (meth)acrylate, trifunctional(meth)acrylate, or tetrafunctional (meth)acrylate is preferable thanmonofunctional (meth)acrylate. Alternatively, a mixture obtained bymixing two or more types of monofunctional to tetrafunctional(meth)acrylate is preferable.

Examples of the monofunctional (meth)acrylate include acrylic acid,(meth)acrylic acids such as methacrylic acid or crotonic acid, laurylacrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate,2-hydroxypropyl acrylate, tetrahydrofurfuryl acrylate, 1,6-hexanediolmonoacrylate, and dicyclopentanediene acrylate.

Examples of the bifunctional (meth)acrylate include 1,3-propanedioldiacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate,1,9-nonanediol diacrylate, diethylene glycol diacrylate, polyethyleneglycol 400 diacrylate, and tripropylene glycol diacrylate.

Examples of the trifunctional (meth)acrylate include triacrylates suchas pentaerythritol triacrylate, trimethylol propane triacrylate,trimethylol propane PO modified triacrylate, or trimethylol propane EOmodified triacrylate, and trimethacrylate thereof.

Examples of the tetrafunctional (meth)acrylate include ditrimethylolpropanetetraacrylate and pentaerythritol tetraacrylate.

Examples of the isocyanate-based crosslinking agent include anisocyanate monomer such as tolylene diisocyanate, chlorophenylenediisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate,isophorone diisocyanate, xylylene diisocyanate, diphenylmethanediisocyanate, or hydrogenated diphenylmethane diisocyanate, and anisocyanate compound in which those isocyanate monomers are added withtrimethylol propane or the like, an isocyanurate compound, a biuret typecompound, and also a urethane prepolymer type isocyanate added withknown polyether polyol, or polyester polyol, acryl polyol, polybutadienepolyol, polyisoprene polyol, or the like.

Examples of the epoxy-based crosslinking agent include ethylene glycolglycidyl ether, polyethylene glycol diglycidyl ether, glycerindiglycidyl ether, glycerin triglycidyl ether, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, N,N,N′,N′-tetraglycidyl-m-xylylene diamine,N,N,N′,N′-tetraglycidyl aminophenylmethane, triglycidyl isocyanurate,m-N,N-diglycidyl aminophenyl glycidyl ether, N,N-diglycidyl toluidine,and N,N-diglycidyl aniline. Examples of the aziridine-based crosslinkingagent include diphenylmethane-4,4′-bis(1-aziridinecarboxamide),trimethylol propane tri-β-aziridinyl propionate, tetramethylol methanetri-β-aziridinyl propionate, toluene-2,4-bis(1-aziridinecarboxamide),triethylenemelamine, bisisophthaloyl-1-(2-methyl aziridine),tris-1-(2-methyl aziridine)phosphine, and trimethylol propanetri-β-(2methyl aziridine)propionate.

Addition amount of the crosslinking agent is, relative to 100 parts bymass of the base polymer, preferably in the range of 0.5 to 25 parts bymass.

(Photocrosslinking Initiator)

As for the photocrosslinking initiator which is used for the outermostsurface layer, any one of the cleave type photocrosslinking initiatorand the hydrogen withdrawing type photocrosslinking initiator can beused like the intermediate layer. In particular, the hydrogenwithdrawing type photocrosslinking initiator is preferable.

As for the hydrogen withdrawing type photocrosslinking initiator, forexample, any one of benzophenone, Michler's ketone, dibenzosuberone,2-ethyl anthraquinone, and isobutyl thioxanthone and derivativesthereof, or a mixture component consisting of combination of two or moretypes thereof can be used. However, the photocrosslinking initiator of ahydrogen withdrawing type is not limited to the materials describedabove. Furthermore, it is also possible to use at various ratios thecleave type photocrosslinking initiator and the hydrogen withdrawingtype photocrosslinking initiator in combination.

Content of the photocrosslinking initiator is not particularly limited,and in general it is preferably adjusted within a range of 0.1 to 5parts by mass relative to 100 parts by mass of the base polymer.However, in view of the balance with other elements, it may be more thanthis range.

Similar to the intermediate layer, the outermost surface layer maycontain an ionomer resin or a tackifying resin, a crosslinking agent, aphotocrosslinking initiator, a silane coupling agent, an anti-oxidant, aweather resistant stabilizer, a processing aid or the like. Among them,it is preferable that a crosslinking agent and/or a photocrosslinkinginitiator are/is contained in the outermost surface layer. Accordingly,for a case in which layering is made with an intermediate layercontaining the crosslinking agent and/or the photocrosslinkinginitiator, an interaction between the 2 layers is caused, thus enablingobtainment of even higher reliability after the attachment.

<Layered Constitution>

The present transparent adhesive material is characterized to have aconstitution that it has at least one layer of each of the intermediatelayer and the outermost surface layer and it is obtained by layeringthose layers for integration. By having such layered constitution, notonly the electrical characteristics or reliability after attachment butalso various characteristics that are required for a transparentadhesive material can be achieved in a balanced manner.

Specific examples of the layered constitution include a 2-layerconstitution of intermediate layer/outermost surface layer and a2-component and 3-layer constitution of outermost surfacelayer/intermediate layer/outermost surface layer. Furthermore, the layernumber may be increased to 4 layers, 5 layers, 6 layers, or 7 layers, ifnecessary. In particular, to have both the electrical characteristicsand various required characteristics like adhesion property or adhesionstrength to a subject for adhesion, it is preferable to have a2-component and 3-layer constitution of outermost surfacelayer/intermediate layer/outermost surface layer in which theintermediate layer with low permittivity is included.

With regard to the total thickness ratio of the intermediate layer andthe outermost surface layer, the value of the intermediate layer (in thecase of having two or more layers of the intermediate layer, their totalthickness)/the outermost surface layer (in the case of having two ormore layers of the outermost surface layer, their total thickness) ispreferably 0.05 to 20, more preferably 0.1 or more or 15 or less, andeven more preferably 0.5 or more or 12 less. As the value of theintermediate layer/the outermost surface layer is within the aboverange, various required characteristics can be easily obtained in abalanced manner.

Furthermore, other layers may be also included, and specific examplesthereof include a transparent inorganic oxide film layer like SiO₂ andAl₂O₃, a barrier film layer, and a retardation film layer for display orthe like. Furthermore, irrespective of the constitution of a transparentadhesive material, a protective film may be layered on a single surfaceor both surfaces of a transparent adhesive material.

(Sheet Thickness)

The lower limit of the thickness of the present transparent adhesivematerial is preferably 10 μm or more, more preferably 30 μm or more, andeven more preferably 50 μm or more. The upper limit is preferably 1 mmor less, more preferably 500 μm or less, and even more preferably 250 μmor less.

By reducing the sheet thickness, it is possible to respond therequirement for having thinning. However, if the thickness is reducedexcessively, for example, it is believed that there is a possibility ofhaving an occurrence of air bubbles around steps with different heightwhen there are irregularities on a surface of a member for attachment.

<Characteristics of the Present Transparent Adhesive Material>

(Relative Permittivity)

For carrying out attachment between a member for constituting an opticaldevice provided with a touch panel function and a transparent adhesivematerial, in particular, when an adhesive sheet is used for attachmentbetween layers with touch panel function or attachment between a layerprovided with a touch panel function and a surface protecting member,the adhesive sheet is required to have a function of an insulatinglayer. From the viewpoint of reducing a loss of an electric signal withhigh frequency like touch signal, the adhesive material is required tohave low relative permittivity.

From this point of view, the present transparent adhesive material hasrelative permittivity of preferably 3.3 or less, more preferably 3.0 orless, and even more preferably 2.8 or less at a frequency of from 100kHz to 1 MHz.

Furthermore, the present transparent adhesive material has relativepermittivity of preferably 3.0 or less, and more preferably 2.8 or lessat a frequency of 1 MHz.

Also with regard to a low frequency region, lower relative permittivitycan allow even higher function of an insulating layer. Namely, it ispreferable to have lower frequency dependency of relative permittivity.From this point of view, the difference (ε (1 MHz)−ε (1 kHz)) betweenrelative permittivity at a frequency of 1 kHz (ε (1 MHz)) and relativepermittivity at a frequency of 1 MHz (ε (1 kHz)) of the adhesivematerial is preferably 1.5 or less, more preferably 1.0 or less, andeven more preferably 0.8 or less. As the ε (1 MHz)−ε (1 kHz) is 1.5 orless, more stabilized electrical characteristics can be exhibited in abroad frequency range.

Furthermore, having a little difference (ε (1 MHz)−ε (1 kHz)) betweenthe relative permittivity at a frequency of 1 kHz (ε (1 MHz)) and therelative permittivity at a frequency of 1 MHz (ε (1 kHz)) means lessfrequency dependency of the relative permittivity, and thus it isexpected that stable electrical characteristics are exhibited in a broadfrequency range.

To have the production such that ε (1 MHz)−ε (1 kHz) is within the aboverange, for example, it is sufficient that the olefinic polymer (A) isused as a base resin of the intermediate layer to have low permittivity.If an acryl-based polymer is used to have low permittivity, ε (1 MHz)−ε(1 kHz) of higher than 1.5 is obtained.

(Holding Property)

For a case of attaching an adhesive material to a member forconstituting an optical device provided with a touch panel function, forexample, it is necessary to have a height difference absorbing propertyat sufficient level, in particular when attachment is made with a memberhaving print height difference. However, it may easily become acharacteristic that is contradictory to the storage stability duringstorage of an adhesive material, in particular, during storage in theform of a roll. In this regard, by having the holding property of theadhesive material in a predetermined value range, those physicalproperties may be obtained in a balanced manner. Furthermore, by havingthe layered constitution, the above physical properties and othervarious physical properties that are derived from electricalcharacteristics can be obtained in a balanced manner.

From this point of view, the lower limit of the deviation amount of thepresent transparent adhesive material according to a holding testincluding a constitution of SUS plate/adhesive material (25×20 mm)/PET,a load of 0.5 kg, a temperature of 40° C., and a time of 30 minutes ispreferably 0.2 mm or more, and more preferably 0.5 mm or more.Furthermore, the upper limit is preferably 20 mm or less, and morepreferably 15 mm or less.

When the deviation amount is excessively small, a sufficient printheight difference is not obtained, air bubbles may occur during anattachment process, or the reliability after the attachment is lowered.On the other hand, when it is excessively high, the end part of thesheet may slip during storage so that poor long-term storage stabilityis yielded.

(Adhesion Property)

To have a good handling property when the present transparent adhesivematerial is attached to a member, it is necessary to have adhesionproperty at certain level after the material is roll-pressed at roomtemperature.

From this point of view, when the present transparent adhesive materialis roll-pressed according to one reciprocation of 2 kg roll on a sodalime glass and then removed by 180° peeling at 60 mm/min and 23° C., thepeeling force is preferably 0.5 N/10 mm or more, and more preferably 1N/10 mm or more. If the peeling force is excessively low, that is, theadhesion property is low, it is difficult to peel a release film fromthe present transparent adhesive material, for example, in the case of aconstitution in which the present transparent adhesive material and arelease film are layered.

(Peeling Force)

When one surface of the present transparent adhesive material is appliedand pressed on a soda lime glass and then removed at peeling rate of 60mm/min at 23° C., the 180° peeling force is preferably 2 N/10 mm ormore, more preferably 4 N/10 mm or more, and even more preferably 6 N/10mm or more.

As the peeling force is within the defined range, it is possible toprovide the present transparent adhesive material with sufficientreliability when the present transparent adhesive material is attachedto a subject for attachment.

(Haze)

The present transparent adhesive material has a characteristic of beingtransparent, and thus it is distinguished from a non-transparentmaterial like a foamed resin sheet, for example. Specifically, when bothsurfaces of the present transparent adhesive material are sandwichedwith a soda lime glass (thickness of 0.5 mm) and then haze is measuredaccording to JIS K7136, it is preferable that the haze is 5% or less.More preferably, the haze is 2% or less, and even more preferably 1% orless.

(Water Vapor Permeability)

It is preferable that the present transparent adhesive material has,when calculated in terms of the thickness of 150 μm, water vaporpermeability of 300 g/m²/day or less at 40° C. and 90% RH from theviewpoint of suppressing introduction of moisture from an outside,protecting an optical device or a peripheral member, and enhancing thereliability. In particular, it is more preferably 150 g/m²/day or less,and even more preferably 100 g/m²/day or less.

Furthermore, in order for the present transparent adhesive material tohave water vapor permeability of 300 g/m²/day or less, it is possiblethat a resin with relatively high water vapor permeability like anethylene-α-olefin copolymer and a styrene-based elastomer is selected asthe olefinic polymer (A) or the thickness ratio of the intermediatelayer and the outermost surface layer or the layer configuration may beadjusted. However, it is not intended to be limited to those methods.

[Method for Producing Transparent Adhesive Sheet]

As the method for producing a transparent adhesive sheet, it is possibleto employ a known method, for example, an extrusion casting method, acalendering method, or an inflation method which has melting and mixingequipment such as a single-screw extruder, a multi-screw extruder, theBanbury mixer, or a kneader and uses a T-die, and they are notparticularly limited. Among them, for the present transparent adhesivematerial, the extrusion casting method is preferably used from theviewpoint of handling properties, productivity, or the like.

The molding temperature in the extrusion casting method using a T-die isappropriately adjusted depending on the flow characteristics,film-forming properties, or the like of the resin composition to beused, but it is preferably from 80 to 230° C., and more preferably from90 to 160° C.

The method for layering each layer constituting a transparent adhesivesheet is not particularly limited, and a method well known in the fieldmay be used. For example, there is a coextrusion method in which, afterperforming layering to a film shape by using a feed block or amulti-manifold die, cold pressing is performed using a chilled roll tohave layering, an extrusion lamination method in which, by using anextruder, a resin composition is melt and extruded into a film shapeusing a T die or the like placed on the tip of an extruder and layeredon a surface of a resin composition which is previously formed as asheet-shaped film, and a heat lamination method in which, afterperforming the layering like the extrusion lamination method, pressingunder heating and adhesion are performed by using a dielectric roll.Among those methods, it is preferable that the layering is performed bya coextrusion method. As the layering is made in a melt state using acoextrusion method, the interface strength between each layer can bestabilized.

Furthermore, in a case in which an extrusion lamination method or a heatlamination method is used, it is preferable that the adhesive layer ispressed after it is first layered on a surface of a release film.

When various kinds of additives such as the silane coupling agent, theanti-oxidant, and the weather resistant stabilizer are used, they may besupplied after being blended in advance together with the resin, or allof the materials may be melted and mixed in advance and then supplied,or only the additives may be concentrated in the resin to prepare amaster batch in advance and then supplied.

In addition, it is preferable to layer a protective film on one surfaceor both surfaces of the transparent adhesive material from the viewpointof preventing blocking between sheets or foreign matter adhesion.Alternatively, embossing processing or various kinds of unevenness (acone shape, a pyramid shape, a hemispherical shape, or the like)processing may be carried out, if necessary. In addition, the surface ofthe transparent adhesive material may be subjected to various kinds ofsurface treatments such as a corona treatment, a plasma treatment, and aprimer treatment for the purpose of improving the adhesion property tovarious kinds of subject for adhesion.

[Layered Body for Constituting Optical Device]

The present transparent adhesive material can be formed into a layeredbody for constituting an optical device by layering a member whichconstitutes an optical device on at least one surface thereof, and anoptical device can be produced using the layered body for constitutingan optical device.

For example, by forming a layered body for constituting an opticaldevice according to attachment of the present transparent adhesivematerial and a member which constitutes an optical device followed bylight irradiation from the side of the member which constitutes anoptical device for photocrosslinking the intermediate layer and theoutermost surface layer, a layered body for constituting an opticaldevice can be produced.

Examples of the light to irradiate may include ionizing radiation suchas α rays, β rays, γ rays, neutron rays, and electron beams, ultravioletlight, and visible light, and among them, ultraviolet light ispreferable. In addition, the irradiating energy, irradiating time, andlight irradiating method are not particularly limited, and thephotocrosslinking may be carried out by activating the photocrosslinkinginitiator.

Furthermore, according to light irradiation of the present transparentadhesive material, a transparent adhesive material having an outermostsurface layer containing a photoreaction product of the acrylic polymer(B) and an intermediate layer, which is adjacent to the outermostsurface layer, containing a photoreaction product of the olefinicpolymer (A) can be formed, for example.

Furthermore, the present transparent adhesive material after lightirradiation has relative permittivity of 3.3 or less at a frequency offrom 100 kHz to 1 MHz as described above. In particular, it may be 3.0or less, or more particularly 2.8 or less. Furthermore, the water vaporpermeability is, when calculated in terms of the thickness of 150 μm,300 g/m²/day or less at 40° C. and 90% RH as described above. Inparticular, it may be 150 g/m²/day or less, or more particularly 100g/m²/day or less. The haze measured according to JIS K7136 can bepreferably 5% or less, more preferably 2% or less, and even morepreferably 1% or less.

Accordingly, by using the present transparent adhesive material afterlight irradiation and a member which constitutes an optical device, anoptical device or a member for constituting an optical device can beproduced. For example, as the present transparent adhesive materialafter light irradiation is layered with a member which constitutes anoptical device and light is irradiated on the transparent adhesivematerial over the member which constitutes an optical device, thetransparent adhesive material is subjected to crosslinking and anoptical device can be also produced.

As the member which constitutes an optical device, a layered bodyconsisting of any one kind or a combination of two or more kindsselected from the group consisting of a touch panel, an image displaypanel, a front surface protective panel, a retardation film, and apolarizing film can be formed. The layered body as a layered body forconstituting an optical device can be used for producing an opticaldevice.

Furthermore, as the member which constitutes an optical device, alayered body consisting of any one kind or a combination of two or morekinds selected from the group consisting of a solar cell, a back surfaceprotective panel, and a front surface protective panel can be formed.The layered body can be used as a member for constituting a solar cellmodule.

Furthermore, as the member which constitutes an optical device, alayered body consisting of any one kind or a combination of two or morekinds selected from the group consisting of a front surface protectivesubstrate, an organic EL element, and a back surface protectivesubstrate can be formed. The layered body can be used as a member forconstituting an organic EL element.

<Description of Terms>

In the invention, in a case in which it is expressed as “X to Y” (X andY are an arbitrary number, respectively), it also encompasses themeaning “preferably greater than X” or “preferably less than Y” as wellas the meaning “X or more and Y or less” unless otherwise stated.

In addition, in a case in which it is expressed as “X or more” (X is anarbitrary number) or “Y or less” (Y is an arbitrary number), it alsoencompasses the meaning of “preferably greater than X” or “preferablyless than Y”.

In general, the “sheet” refers to a thin flat product having arelatively small thickness compared to the length and width according tothe definition by JIS, and generally the “film” refers to a thin flatproduct which has an extremely small thickness compared to the lengthand width and of which the maximum thickness is arbitrarily limited, andis typically provided in the form of a roll (Japanese IndustrialStandards JIS K6900). For example, with regard to the thickness, thosehaving 100 μm or more are referred to as a sheet and those having lessthan 100 μm are referred to as a film in narrow sense. However, theboundary between the sheet and the film is not clear and it is notrequired to distinguish the two in words in the invention, and thus itis intended to include the “sheet” even when referred to as the “film”and to include the “film” even when referred to as the “sheet” in theinvention.

EXAMPLES

Hereinbelow, the invention will be described in more detail withreference to Examples. However, it is evident that the invention is notlimited by Examples.

[Composition 1 for Forming Intermediate Layer]

To 1 kg of ethylene-butene random copolymer A-1 (density: 870 kg/m³,weight average molecular weight (Mw): 100,000, MFR (190° C., 21.18 N):35 g/10 min, relative permittivity at 100 kHz: 2.3, relativepermittivity at 1 MHz: 2.3), butene content: 14% by mol, crystal fusionpeak temperature: 55° C., crystal fusion heat: 53 J/g) as the olefinicpolymer (A), 50 g of silane modified ethylene-octene random copolymerA-3 (density: 868 kg/m³, melting point: 54° C., MFR (190° C., 21.18 N):1.7 g/10 min, weight average molecular weight (Mw): 250,000, relativepermittivity at 100 kHz: 2.3, relative permittivity at 1 MHz: 2.3), 30 gof isobornyl methacrylate (manufactured by SHIN-NAKAMURA CHEMICAL CO.,LTD., NK Ester IB) and 20 g of 1,10-decanediol dimethacrylate(manufactured by SHIN-NAKAMURA CHEMICAL CO., LTD., NK Ester DOD-N) as acrosslinking agent, and 15 g of a mixture of 2,4,6-trimethylbenzophenone and 4-methyl benzophenone (manufactured by Lanberti S.p.A.,ESACURE TZT) as a photocrosslinking initiator were added to prepare acomposition 1 for forming an intermediate layer.

The composition 1 for forming an intermediate layer had 130° C. meltviscosity of 9.9×10² Pa·s, relative permittivity of 2.3 at a frequencyof 100 kHz, and relative permittivity of 2.3 at a frequency of 1 MHz.

[Composition 2 for Forming Intermediate Layer]

By mixing 1 kg of A-1 as the olefinic polymer (A) with 30 g of isobornylmethacrylate and 20 g of 1,10-decanediol dimethacrylate as acrosslinking agent, and 15 g of a mixture of 2,4,6-trimethylbenzophenone and 4-methyl benzophenone as a photocrosslinking initiator,a composition 2 for forming an intermediate layer was prepared.

The composition 2 for forming an intermediate layer had 130° C. meltviscosity of 5.7×10² Pa·s, relative permittivity of 2.3 at a frequencyof 100 kHz, and relative permittivity of 2.3 at a frequency of 1 MHz.

[Composition 3 for Forming Intermediate Layer]

By using 1 kg of A-1 as the olefinic polymer (A) and without mixing witha crosslinking agent and a photocrosslinking initiator, a composition 3for forming an intermediate layer was prepared.

The composition 3 for forming an intermediate layer had 130° C. meltviscosity of 6.0×10² Pa·s, relative permittivity of 2.3 at a frequencyof 100 kHz, and relative permittivity of 2.3 at a frequency of 1 MHz.

[Composition 4 for Forming Intermediate Layer]

To 1 kg of ethylene-butene random copolymer A-2 (density: 864 kg/m³, MFR(190° C., 21.18 N): 3.6 g/10 min, weight average molecular weight (Mw):200,000, relative permittivity at 100 kHz: 2.3, relative permittivity at1 MHz: 2.3), butene content: 16% by mol, crystal fusion peaktemperature: 40° C., crystal fusion heat: 45 J/g), 30 g of isobornylmethacrylate and 20 g of 1,10-decanediol dimethacrylate as acrosslinking agent, and 15 g of a mixture of 2,4,6-trimethylbenzophenone and 4-methyl benzophenone as a photocrosslinking initiatorwere added to prepare a composition 5 for forming an intermediate layer.

The composition 4 for forming an intermediate layer had 130° C. meltviscosity of 6.4×10³ Pa·s, relative permittivity of 2.3 at a frequencyof 100 kHz, and relative permittivity of 2.3 at a frequency of 1 MHz.

[Composition 1 for Forming Outermost Surface Layer]

To 1 kg of acrylic acid ester copolymer B-1 (weight average molecularweight (Mw): 400,000) obtained by random copolymerization of 77 parts bymass of 2-ethylhexyl acrylate, 19 parts by mass of vinyl acetate, and 4parts by mass of acrylic acid, 20 g of isobornyl methacrylate (Mw: 222)and 15 g of a photocrosslinking initiator (manufactured by LanbertiS.p.A., ESACURE TZT) consisting of a mixture of 2,4,6-trimethylbenzophenone and 4-methyl benzophenone were added to prepare acomposition 1 for forming an outermost surface layer.

The composition 1 for forming an outermost surface layer had 130° C.melt viscosity of 2.4×10² Pa·s, relative permittivity of 3.5 at afrequency of 100 kHz, and relative permittivity of 3.2 at a frequency of1 MHz.

[Composition 2 for Forming Outermost Surface Layer]

To 1 kg of acrylic acid ester copolymer B-1 (weight average molecularweight (Mw): 400,000), 15 g of a mixture of 2,4,6-trimethyl benzophenoneand 4-methyl benzophenone as a photocrosslinking initiator was added toprepare a composition 2 for forming an outermost surface layer.

The composition 2 for forming an outermost surface layer had 130° C.melt viscosity of 2.8×10² Pa·s, relative permittivity of 3.5 at afrequency of 100 kHz, and relative permittivity of 3.2 at a frequency of1 MHz.

[Composition 3 for Forming Outermost Surface Layer]

To 1 kg of acrylic acid ester copolymer B-1 (weight average molecularweight (Mw): 400,000) obtained by random copolymerization of 77 parts bymass of 2-ethylhexyl acrylate, 19 parts by mass of vinyl acetate, and 4parts by mass of acrylic acid, 20 g of 1,10-decanediol dimethacrylate(Mw: 310) as a crosslinking agent and 15 g of a mixture of2,4,6-trimethyl benzophenone and 4-methyl benzophenone as aphotocrosslinking initiator were added to prepare the composition 1 forforming an outermost surface layer.

The composition 1 for forming an outermost surface layer had 130° C.melt viscosity of 2.5×10² Pa·s, relative permittivity of 3.5 at afrequency of 100 kHz, and relative permittivity of 3.2 at a frequency of1 MHz.

Example 1

The composition 1 for forming an outermost surface layer/the composition1 for forming an intermediate layer/the composition 1 for forming anoutermost surface layer were coextruded at 130° C. to have a sheet shapesuch that each layer has thickness of 37.5 μm/75 μm/37.5 μm. After that,both surfaces of the sheet were covered with two pieces of apolyethylene terephthalate film which has been subjected to a peelingtreatment (DIAFOIL MRA manufactured by Mitsubishi Plastics, Inc.,thickness of 100 μm, and DIAFOIL MRF75 manufactured by MitsubishiPlastics, Inc., thickness of 75 μm). After that, on both surfaces viathe releasing PET, ultraviolet rays of 365 nm were irradiated to havecumulative light amount of 1000 mJ/cm² by using a high pressure mercurylamp. As a result, a transparent adhesive sheet (thickness of 150 μm)was produced.

Example 2

The composition 2 for forming an outermost surface layer/the composition2 for forming an intermediate layer/the composition 2 for forming anoutermost surface layer were coextruded at 130° C. to have a sheet shapesuch that each layer has thickness of 37.5 μm/75 μm/37.5 μm. After that,both surfaces of the sheet were covered with two pieces of apolyethylene terephthalate film which has been subjected to a peelingtreatment (DIAFOIL MRA and DIAFOIL MRF75). After that, on both surfacesvia the releasing PET, ultraviolet rays of 365 nm were irradiated tohave cumulative light amount of 1000 mJ/cm² by using a high pressuremercury lamp. As a result, a transparent adhesive sheet (thickness of150 μm) was produced.

Example 3

The composition 3 for forming an outermost surface layer/the composition2 for forming an intermediate layer/the composition 3 for forming anoutermost surface layer were coextruded at 130° C. to have a sheet shapesuch that each layer has thickness of 60 μm/30 μm/60 μm. After that,both surfaces of the sheet were covered with two pieces of apolyethylene terephthalate film which has been subjected to a peelingtreatment (DIAFOIL MRA and DIAFOIL MRF75). After that, on both surfacesvia the releasing PET, ultraviolet rays of 365 nm were irradiated tohave cumulative light amount of 1000 mJ/cm² by using a high pressuremercury lamp. As a result, a transparent adhesive sheet (thickness of150 μm) was produced.

Comparative Example 1

The composition 2 for forming an outermost surface layer/the composition3 for forming an intermediate layer/the composition 2 for forming anoutermost surface layer were coextruded at 130° C. to have a sheet shapesuch that each layer has thickness of 37.5 μm/75 μm/37.5 μm. After that,both surfaces of the sheet were covered with two pieces of apolyethylene terephthalate film which has been subjected to a peelingtreatment (DIAFOIL MRA and DIAFOIL MRF75). After that, on both surfacesvia the releasing PET, ultraviolet rays of 365 nm were irradiated tohave cumulative light amount of 1000 mJ/cm² by using a high pressuremercury lamp. As a result, a transparent adhesive sheet (thickness of150 μm) was produced.

Comparative Example 2

The composition 2 for forming an outermost surface layer/the composition4 for forming an intermediate layer/the composition 2 for forming anoutermost surface layer were coextruded at 130° C. to have a sheet shapesuch that each layer has thickness of 37.5 μm/75 μm/37.5 μm. After that,both surfaces of the sheet were covered with two pieces of apolyethylene terephthalate film which has been subjected to a peelingtreatment (DIAFOIL MRA and DIAFOIL MRF75). After that, on both surfacesvia the releasing PET, ultraviolet rays of 365 nm were irradiated tohave cumulative light amount of 1000 mJ/cm² by using a high pressuremercury lamp. As a result, a transparent adhesive sheet (thickness of150 μm) was produced.

Comparative Example 3

Only the composition 1 for forming an intermediate layer was formed intoa sheet shape such that it has thickness of 150 μm. After that, bothsurfaces of the sheet were covered with two pieces of a polyethyleneterephthalate film which has been subjected to a peeling treatment(DIAFOIL MRA and DIAFOIL MRF75) to produce a transparent adhesive sheet(thickness of 150 μm).

<Evaluation>

The following physical properties were evaluated for the transparentadhesive sheets obtained from above Examples and Comparative Examples.

(Adhesion Property)

The sheet produced in each of Examples and Comparative Examples wasroll-pressed according to one reciprocation of a 2 kg roll on a sodalime glass, and then the peeling force at the time of removal by 180°peeling at 60 mm/min and 23° C. was immediately measured.

The sheet with less than 0.5 N/10 mm was determined as “×” and the sheetwith 0.5 N/10 mm or more was determined as “◯”.

(Peeling Force)

The release film on one surface of the sheet produced in each ofExamples and Comparative Examples was peeled and then attached with a 50μm PET film (DIAFOIL T100 manufactured by Mitsubishi Plastics, Inc., 50μm) as a backing film. The layered product was cut to have a length of150 mm and a width of 10 mm. After that, the remaining release film waspeeled off, and then the adhesive surface exposed by peeling wasroll-pressed on a soda lime glass. The attached product was subjected toan autoclave treatment (80° C., gauge pressure of 0.3 MPa, 20 minutes)for finishing adhesion. The resulting sample was irradiated from the PETfilm surface side with ultraviolet rays of 365 nm to have cumulativelight amount of 2000 mJ/cm² by using a high pressure mercury lamp.According to aging for 15 hours at 23° C. and 50% RH, a sample formeasuring adhesion force was prepared.

The peeling force (N/10 mm) was then measured when the sample is removedat peeling angle of 180° and peeling rate of 60 mm/min.

(Relative Permittivity)

The release film on one side of the sheet produced in each of Examplesand Comparative Examples was peeled and then roll-pressed to a SUSplate. After that, by performing an autoclave treatment (80° C., gaugepressure of 0.3 MPa, 20 minutes), the sheet was adhered. Next, afterpeeling the remaining release film followed by roll-press of an aluminumfoil of 45 mmϕ, a sample for measuring relative permittivity wasprepared. At that time, for Comparative Example 3, the release film onboth sides was removed, and according to vacuum vapor deposition of thealuminum electrode to have 45 mmϕ on both surfaces of the sheet, asample for measuring relative permittivity was prepared.

By using the sample for measuring relative permittivity, the relativepermittivity at 23° C., 50% RH, and a frequency of from 1 kHz to 1 MHzwas measured based on JIS C2138 by using a LCR meter (HP4284Amanufactured by Agilent Technologies, Inc.).

(Haze)

The release film of the sheet was peeled in order and the sheet wassubjected to roll-attachment on the front and back surfaces of a sodalime glass (82 mm×53 mm×0.5 mm thickness). The attached product wassubjected to an autoclave treatment (80° C., gauge pressure of 0.3 MPa,20 minutes) for finishing adhesion. Then, the sheet was irradiated withultraviolet rays of 365 nm to have cumulative light amount of 2000mJ/cm² by using a high pressure mercury lamp. According to aging for 15hours at 23° C. and 50% RH, a sample for measuring opticalcharacteristics was prepared. For the sample, the haze value based onJIS K7136 was obtained by using a haze meter (NDH5000 manufactured byNIPPON DENSHOKU INDUSTRIES Co., LTD.).

TABLE 1 Comparative Comparative Example 1 Example 2 Example 3 Example 1Example 2 Compar- Inter- Inter- Inter- Inter- Inter- ative mediateSurface mediate Surface mediate Surface mediate Surface mediate SurfaceExample 3 layer layer layer layer layer layer layer layer layer layerMonolayer Composition (A) Olefin-based A-1 100 100 100 100 100 A-2 100A-3 5 5 A-4 (B) Acryl-based B-1 100 100 100 100 100 Crosslinking agentIB 3 2 3 3 3 3 DOD-N 2 2 2 2 2 2 UV initiator TZT 1.5 1.5 1.5 1.5 1.51.5 1.5 1.5 1.5 1.5 130° C. Melt Pa · s 990 240 570 280 570 250 600 2806400 280 990 viscosity η ηa/ηb — 4.1 2 2.3 2.1 22.9 — Adhesion 23° C.Roll press ○ ○ ○ ○ ○ x property Peeling force N/10 mm 11 5 9 1 1 18Relative 1 kHz 3.0 3.0 4.1 3.7 3.0 2.3 permittivity ε 100 kHz 2.8 2.83.3 3.4 2.8 2.3 1 MHz 2.6 2.6 2.9 3.2 2.6 2.3 ε(1 kHz)-ε(1 MHz) 0.4 0.41.2 0.5 0.4 0 Water vapor g/m²/day #150 Cup ⊚ (35) ⊚ (34) ○ (105) ⊚ (34)⊚ (32) ⊚ (19) permeability method Haze (%) #150 0.4 0.4 0.3 0.9 0.3 0.8

The sheets produced in Examples 1 to 3 were found to have excellentdielectric characteristics while they satisfy the adhesion property,peeling force, optical characteristics, and the like that are requiredfor a transparent adhesive sheet.

On the other hand, since no crosslinking agent or photocrosslinkinginitiator is used in the intermediate layer of Comparative Example 1,diffusion and permeation of the crosslinking agent contained in theintermediate layer, a reaction between the crosslinking agent containedin the intermediate layer and the resin composition constituting theoutermost surface layer, or the like did not occur, and an interactionbetween the intermediate layer and the outermost surface layer was alsowas unlikely to occur. Thus, the interlayer strength was significantlylowered, and during the peeling test, peeling easily occurred betweenthe layers even by weak force.

In Comparative Example 2, the intermediate layer has high melt viscosityand also the difference in melt viscosity of the outermost surface layeris very high, and thus a sufficient interface adhesion property cannotbe obtained at the time of layering the intermediate layer and theoutermost surface layer, and similar to Comparative Example 1, peelingeasily occurred between the layers even by weak force during the peelingtest.

In Comparative Example 3, the composition for intermediate layer wasused as monolayer so that, as an adhesive sheet, the adhesion propertyat room temperature was insufficient, and also as an adhesive sheet, thehandling property was poor.

According to the above Examples and Comparative Examples as well as theresults of the test which has been carried out until now by the presentinventors, with regard to the transparent adhesive material providedwith an outermost surface layer containing an acrylic polymer (B) and aphotocrosslinking initiator, and an intermediate layer containing anolefinic polymer (A), a crosslinking agent, and a photocrosslinkinginitiator, if the intermediate layer contains a (meth)acrylate monomeras the crosslinking agent and has relative permittivity of 3.0 or lessat a frequency of from 100 kHz to 1 MHz, and also the 130° C. meltviscosity of the resin composition which constitutes the outermostsurface layer and the intermediate layer is 5×10¹ to 5×10³ Pa·s and theratio η_(a)/η_(b) of the melt viscosity η_(a) of the outermost surfacelayer and the melt viscosity η_(b) of the intermediate layer is 0.05 to20, it can be considered that low relative permittivity and excellentadhesion characteristics can be obtained and also the intermediate layerand the outermost surface layer can be suitably integrated.

1. A photocrosslinkable transparent adhesive material, comprising: anoutermost surface layer comprising a photoreaction product of an acrylicpolymer (B); and an adjacent intermediate layer comprising aphotoreaction product of an olefinic polymer (A), wherein relativepermittivity of the photocrosslinkable transparent adhesive material is3.3 or less at a frequency of from 100 kHz to 1 MHz.
 2. Thephotocrosslinkable transparent adhesive material according to claim 1,wherein water vapor permeability at 40° C. and 90% RH is 300 g/m²/day orless when calculated in terms of thickness of 150 μm.
 3. Thephotocrosslinkable transparent adhesive material according to claim 1,wherein haze measured based on JIS K7136 is 5% or less.
 4. A method forproducing a layered body for an optical device, the method comprising:attaching the photocrosslinkable transparent adhesive material accordingto claim 1 on a member which constitutes an optical device; andirradiating the transparent adhesive material with light over the memberto cure the photocrosslinkable transparent adhesive material.